The present invention relates to a television receiving apparatus capable of receiving a television broadcasting signal in correspondence to two different kinds of channel plans, and more particularly to a television receiving apparatus having an automatic discrimination auto-search function for two kinds of channel plans.
Conventionally, a television receiving apparatus has been provided which is capable of receiving selectively either the TV (television wave) broadcasting or the CATV (cable television) broadcasting. This television receiving apparatus may have an automatic discrimination auto-search function for automatically discriminating whether the receivable channel plan is for TV broadcasting or for CATV broadcasting (e.g., the Unexamined Japanese Patent Application Publication No. Hei 11-4388).
As disclosed in this publication, noticing that the CATV broadcasting has the channels assigned in a specific frequency band (e.g., 300 MHz to 400 MHz) in which none of the TV broadcasting channels are assigned, a CATV mode is discriminated if any broadcasting station exists in the specific frequency band, or a TV mode is discriminated if no broadcasting station exists in the specific frequency band. And in accordance with a result of discrimination, the channel preset is executed, and the channel tuning control is performed, based on the content of the channel preset.
In this way, the conventional television receiving apparatus discriminates a CATV mode or a TV mode in such a manner that the CATV mode is discriminated if a station exists in a specific frequency band in which the TV broadcasting channel is not assigned.
However, with such a conventional discrimination method, since a station may be discriminated to be present due to the influence of the noise, in spite of the station being absent, there is the possibility that a false discrimination may occur by falsely discriminating the CATV mode in spite of the TV mode in essence. Therefore, to reduce such false discrimination as least as possible, the CATV mode may be discriminated in the case where two or more stations exist in a specific frequency band, but in anyway, it is impossible to eliminate the influence of the noise completely.
This device has been created to solve the above-mentioned problems, and its objective is to provide a television receiving apparatus having improved discrimination accuracy in an automatic discrimination auto-search mode.
In order to solve the above-mentioned problems, a television receiving apparatus of this device capable of receiving signals of a desired frequency in correspondence to a first channel plan having predetermined channel frequencies assigned, and a second channel plan containing the channel frequencies assigned to this first channel plan and having other channel frequencies assigned in a frequency band not assigned to this first channel plan, comprising channel number counting means for counting up the number of station present channels in the channel plan to which a station belongs, if it is judged that the channel frequency of the station is within a fixed frequency range from a center frequency.
In the present device having the above feature, the channel number counting means judges whether or not the channel frequency of a station is within a fixed frequency range from the center frequency, and counts up the number of station present channels in the channel plan to which the station belongs, if the channel frequency of the station is within the fixed frequency range from the center frequency. In this way, in this device, the number of station present channels contained in each channel plan is counted by judging whether or not the channel frequency of the station is within the fixed frequency range from the center frequency during the automatic discrimination auto-search for the channel plan, so that the number of channels can be counted more correctly.
A television receiving apparatus of this device which is capable of receiving signals of a desired frequency in correspondence to a first channel plan having predetermined channel frequencies assigned, and a second channel plan containing the channel frequencies assigned to the first channel plan and having other channel frequencies assigned in a frequency band not assigned to the first channel plan, comprising:
station presence judging means for judging whether a broadcasting station is present or not at a channel frequency assigned to each channel plan by searching all or part of the frequency bands contained in the first channel plan or the second channel plan;
channel number counting means for judging whether or not the channel frequency of the broadcasting station is within a fixed frequency range from a center frequency, if the station presence judging means judges that the broadcasting station is present, and counting up the number of station present channels in the channel plan to which the broadcasting station belongs, if the channel frequency of the broadcasting station is within the fixed frequency range from the center frequency, for all the broadcasting stations which are judged that station is present; and
channel plan discriminating means for comparing the number of channels for the first channel plan and the number of channels for the second channel plan which are counted by the channel number counting means, discriminating a first channel plan mode, if the count number for the first channel plan is greater than or equal to the count number for the second channel plan, or discriminating a second channel plan mode, if the count number for the first channel plan is smaller than the count number for the second channel plan.
In this device having the above feature, the station presence judging means searches all the frequency bands contained in the first channel plan or the second channel plan substantially continuously, and judges whether or not a broadcasting station exists at a channel frequency assigned to each channel plan. When this station presence judging means judges that the broadcasting station is present, the channel number counting means judges whether or not the channel frequency of that broadcasting station is within a fixed frequency range from the center frequency, and counts up the number of station present channels in the channel plan to which the broadcasting station belongs, if the channel frequency of the broadcasting station is within the fixed frequency range from the center frequency, for all the stations which are judged that station is present. Thereafter, the channel plan discriminating means compares the number of channels for the first channel plan and the number of channels for the second channel plan which are counted by the channel number counting means, discriminates a first channel plan mode, if the count number for the first channel plan is greater than or equal to the count number for the second channel plan, or discriminates a second channel plan mode, if the count number for the first channel plan is smaller than the count number for the second channel plan. In this way, in this device, since the number of station present channels contained in each channel plan is counted during the automatic discrimination auto-search for the channel plan, and ultimately the channel plan is discriminated depending on whether the total number of channels for the first channel plan is greater than or equal to the total number of channels for the second channel plan or not, whereby it is possible to eliminate the influence of the noise and discriminate the channel mode at high accuracy.
In the television receiving apparatus of this device, the first channel plan is ground wave broadcasting, and the second channel plan is cable television broadcasting. In a channel plan (TV channel plan) for ground wave broadcasting and a channel plan (CATV channel plan) for CATV broadcasting, the channel frequencies of the channel numbers xe2x80x9c2xe2x80x9d to xe2x80x9c13xe2x80x9d for TV broadcasting are the same as the channel frequencies of the channel numbers xe2x80x9c2xe2x80x9d to xe2x80x9c13xe2x80x9d for CATV broadcasting, and the channel frequencies of the channel numbers xe2x80x9c14xe2x80x9d to xe2x80x9c69xe2x80x9d for TV broadcasting are higher by 2 MHz than the channel frequencies of the channel numbers xe2x80x9c65xe2x80x9d to xe2x80x9c94xe2x80x9d and xe2x80x9c100xe2x80x9d to xe2x80x9c125xe2x80x9d for CATV broadcasting. Also, the channel frequencies of the channel numbers xe2x80x9c14xe2x80x9d to xe2x80x9c64xe2x80x9d for CATV broadcasting are in the frequency bands not assigned to the TV broadcasting. Namely, the CATV channel plan includes the channel frequencies equal or close to the channel frequencies assigned to the TV channel plan, and the channel frequencies in the frequency bands not assigned to this TV channel plan.
In a television receiving apparatus of this device, with the above-described configuration, the channel plan discriminating means discriminates whether or not there is a continuous channel among the channels which are judged that station is present, if the count number for the first channel plan is smaller than the count number for the second channel plan, and discriminating a second channel plan mode only if there is the continuous channel, or discriminating a first channel plan mode, if there is no continuous channel. Namely, in the CATV channel plan that is the second channel plan, because the continuous channel necessarily exists, the continuity of the channel is determined if the CATV mode is discriminated based on the comparison of whether the count number for the first channel plan is smaller than the counter number for the second channel plan, so that the discrimination between the TV mode and the CATV mode can be made more correctly.
In the television receiving apparatus of this device, with the above configuration, the channel number counting means stores the error data off the center frequency in a memory, if it is judged that the channel frequency of the station which is judged to be present is outside a fixed frequency range from the center frequency, for all the stations which are judged to be present in the second channel plan. And if the error data for all the stations are stored in the memory, the error data stored in the memory are compared successively to determine whether or not the difference between the error data and the error data is within a fixed frequency range, and classified into some groups, and the number of error data contained in the largest group is further added and counted up to the number of station present channels for the second channel plan. Namely, this device additionally has a procedure (error data check process) for determining whether or not to count up, as the station present in the second channel plan, the station that is not counted as the station present at that time, because the frequency of the station is outside a fixed frequency from the center frequency, though the station has been judged to be present. Thereby, even when the second channel plan is shifted from a normal frequency, it is possible to count up the station as the broadcasting station that is contained in the second channel plan by performing an error data check process, and to effect discrimination between the TV mode and the CATV mode more correctly.
This error data check process will be discussed below in more detail. The channel number counting means performs a process of storing the error data off the center frequency in a memory when it is judged that the channel frequency of the station that is judged to be present is outside a fixed frequency range from the center frequency, for all the stations for the second channel plan which are judged to be present. And the error data first stored in the memory is set as the reference error data, the error data subsequently stored in the memory is set as the comparative error data, and the comparative error data is compared in succession with the reference error data. When the comparative error data is within a fixed frequency range with respect to the reference error data, the comparative error data is determined to be contained within the same group as the reference error data, and the coincidence number is counted up. On the other hand, when the comparative error data is outside the fixed frequency range with respect to the reference error data, it is checked whether or not the next reference error data has been already registered. If not registered, the comparative error data is registered as the next reference error data. Once the next reference error data is registered, the next reference error data is not registered until the current reference error data has been compared with all the comparative error data (i.e., the counting up for one group has been completed). The channel number counting means performs the above process until the comparison between the reference error data first stored in the memory and the comparative error data subsequently stored in the memory has been completed, and the coincidence number for one group is counted up.
Thereafter, the next reference error data registered before and the first error data stored as the comparative error data are compared in the same way as described above, and the coincidence number for another one group is counted up, until the next reference error data is not registered anymore. Thereby, ultimately, there are produced the groups by the number that the next reference error data has been registered. The coincidence number for the largest group among the acquired groups is further added and counted up to the number of station present channels in the second channel plan. Herein, every time the next group is acquired for one group, the comparison is made between both groups, and the group having a greater number of station preset channels is only left behind. In this way, at the time when the error data check process has been ended, only the group having the greatest coincidence number is left behind.
The fixed frequency range as above may be desirably xc2x1200 kHz, because the error data has relatively common discrepancy. Specifically, one step is set to 27.965 kHz, and the frequency may be changed in a range of xc2x18 steps (i.e., xc2x1223.72 kHz) to effect grouping of the error data.